A curtain (sometimes known as a drape, mainly in the United States) is a piece of cloth intended to block or obscure light, or drafts, or water in the case of a shower curtain. Curtains hung over a doorway are known as portières. Curtains are often hung on the inside of a building's window to block the travel of light, for instance at night to aid sleeping, or to stop light from escaping outside the building (stopping people outside from being able to see inside, often for privacy reasons).